Steve Coy's Contribution Regarding Beamed PowerSteve Coy has contributed this note
to the discussion of powering a "lifter" to geosynchronous orbit. As
the president of MZA Associates, Steve is an expert in the field of modern
optics.
He makes one very important point in his letter below:
that less and less power will be required as the "lifter" climbs the
"beanstalk". At a distance of one Earth radius above the ground, the
"lifter" will only need one-fourth of the power it would require at
the Earth's surface, since the gravitational attraction will be only one-fourth
what it is at ground level... that is, one-fourth gee. At two Earth radii, it
will require only one-ninth the power it will need at the beginning of its
climb.

Hola Roberto,

Have you looked at
using laser or microwave power-beaming for space elevator lifters? Either way,
we should be able to achieve close to diffraction limited spot size at the
lifter receiver antenna, in which case an antenna of diameter 2*lambda*z/D
should suffice to capture 90+% of the power. (Here, lambda = wavelength, in
meters, and D = diameter of the antenna, also in meters.) Suppose we use a laser
operating at a near-infrared wavelength of 1.0 micron (10-6 meters or
10,000 Angstroms); to capture 90+% of the energy broadcast from the ground when
the receiver is at geosynchronous altitude, we need to satisfy the following:

D_rcvr * D_transmitter >= 2 X
10-6 * 3.6 X 107 = 72 (m2)

If both the
transmitting aperture and the receiver antenna are chosen to be the same size,
they'd need to be 8.5m in diameter - that implies a pretty big telescope on the
ground, but smaller than some already existing, and a lot smaller than some
proposed. At the receiver, all we need is a 2-d array of photoelectric cells,
which can be pretty light. We can make either the telescope or the receiver
antenna smaller if we make the other bigger. Also, it's not really necessary to
capture such a large fraction of the energy all the way out to synchronous,
because the power required drops off with altitude due to decreasing
gravity.

PS: to achieve close to diffraction-limited performance at optical wavelengths,
we'd need to use "adaptive optics", to compensate for the optical
effects of atmospheric turbulence, but this is a relatively easy case for it,
because we can set up a cooperative "beacon". I'm less familiar with
microwave power-beaming systems; obviously the transmitter would need to be a
lot bigger, in inverse proportion to the wavelength, but I believe its perfectly
feasible to construct very large microwave phased arrays, they have much higher
operating efficiency, you don't need adaptive optics, and clouds are less of a
problem.

Hasta la email,

Steve

Leon Hansen's
Insightful Remarks Concerning William Sidis."I
just browsed through your article on human intelligence, i.e. the sections
featuring William
Sidis. If you had read the Sarah Sidis' "Sidis Story" carefully,
you would remember her commenting that she was astounded he learned Latin at 2
since in her opinion he began to talk late. I understand your point about the
New York Times and am fully aware of the fact that, in terms of language, others
should greater precocity than young Sidis. However, he was not subject to any
pressure until his adolescence when he entered Harvard at 11. He passed the
Harvard Med School and M.I.T. examinations at 8 but was only admitted due to his
father's influence. His father, Boris Sidis, was a genius as well, who knew 27
languages and wrote excellent works on social psychology. Despite the
possibility of a genetic inheritance, I believe that his educational methods were
primarily responsible for his son's brilliance. Sadly, even today his method
remains not understood. It is common knowledge that people learn best at an
early age. He reasoned that instead of teaching them silly nursery rhymes you could
attempt to interest them in more intellectual matters. Their own curiosity
will then drive them. Since now and then people share a general dislike for
learning, because it means forcefully stuffing their heads with knowledge to
them, Sidis' method remains controversial. It wasn't until M.I.T. professor
Comstock predicted young Sidis to be the greatest mathematician of the century
and a combination of envy and his supposed failure to live up to that claim that
the failure myth came about. I do not doubt that he lived as an eccentric
throughout his later years, but he nonetheless produced fabulous works on
history and contemporary politics. There is evidence of other genius's early
education influencing their intelligence, i.e. Hypathia and Pascal. However,
there is evidence against this found in geniuses such as Newton. Attempts of
influencing intelligence through early education have not been exclusively
unsuccessful and I believe that if Boris Sidis' method were properly understood
this would further hold true."